Programmatically set the value of a type="file" input HTML element? [duplicate]

Question

Note:

The answer(s) below reflect the state of legacy browsers in 2009. Now you can actually set the value of the file input element dynamically/programatically using JavaScript in 2017.

See the answer in this question for details as well as a demo:
How to set file input value programatically (i.e.: when drag-dropping files)?

What I need to do is to programmatically send a POST request to a service from javascript code from an application that uses a .NET WebBrowser, which is basically an embedded Internet Explorer. This service requires one of the fields to be a "file".

So either, is there any way to set the value of a "file" input in a form, given that I have the content of the file, such as in an array of bytes (and not the path of the file; I'm not trying to steal files from users here :) ).

Or perhaps a way to explicitly create and send the POST request instead of creating a FORM dynamically?

I need to use JavaScript code that will be run in my WebBrowser (think IE). Is this possible?

Answer 1

Unfortunately this is not possible as it would be a security issue. Javascript control over file input fields is very limited. Otherwise people could use this to steal files from user's computers.

Since you have control over the browser, you can send the file using a normal HTTPWebRequest, but it can't be done in JavaScript.